The present invention relates to an image reading apparatus and method for correcting a read image suitable for reading bound documents such as books, magazines and the like.
In recent years, image forming apparatuses called book scanners have been commercialized. In these book scanners, an image sensing unit is arranged above a document platen, and an open space of a size adequate to accommodate the placement of a book document or sheet document at a reading position is provided between said document platen and said image sensing unit. When a book document is read by such a book scanner, a user first places the book document on the document platen in an opened faced state so that the reading object surface (document surface) is visible (i.e., facing upward). Thus, a user places the closed book on the document platen and opens the book and turns the pages. Book documents refer not only to bound documents (i.e., bound document comprising a plurality of sheets of paper) such as books and magazines and the like, but also include filed documents.
When a user places a book document on the document platen with the document surface facing upward and presses the start key, scanning of the document is started by the image sensing unit arranged above the document platen, and the read image is successively output to an image output device in parallel to the scanning of the document. Such an image output device may be, for example, a digital copier or printer or the like capable of forming a copy image of the read image.
A user must press both edges of the book document in order to hold the book document in an open-faced conditions during image reading. In the case of thick book documents, this operation is inevitably required. Accordingly, the image sensing unit disposed above the document platen also reads the fingers and hands of the user pressing both edges of the book document along with the document image. It is obvious that when this read image is output to an image output device such as a printer, the printout of the output image will have a superior appearance if the unnecessary images corresponding to fingers and hands of the user can be erased.
Prior art related to methods for erasing such unnecessary images is well known, e.g., U.S. Pat. No. 5,377,019. In the related art, a document image is read in color by a color image sensing device, e.g., a color line charge-coupled device (CCD) and images of the user skin color are eliminated from the read image. Furthermore, the document portion within the read image is discriminated based on the document size detection result, and the pixel density is checked of the entirety or part of the edge region (i.e., blank region) of the document portion, and the images comprising pixels above a constant density, i.e., above a fixed value, are discriminated as unnecessary images and erased.
FIGS. 19A through 19C are illustrations of the disadvantages of the conventional art.
In the aforesaid method for extracting unnecessary images by color discrimination, errors readily occur in the extraction or the unnecessary images due to the difficulty in setting the skin color range of users.
On the other hand, in methods which extract unnecessary images present within the edge region of the document portion by simple density discrimination, the detection object region A8 of the unnecessary image must be limited to the white space on the periphery of document 90 so as to avoid erasure of the necessary image, as shown in FIG. 19A. That is, the detection object region A8 must be set so as to not overlap the print region A7 comprising printed text or graphics. Therefore, when a document has a relatively large area of white space on the periphery of the document as shown in FIG. 19B, or when the majority of a page is blank as shown in FIG. 19C, the finger of a user may protrude from the detection object region A7 even though the user presses down the book document without obscuring the image region of text of graphics, such that the images Gh of the finger tip will remain in output images G91 and G92. Furthermore, headers, images of handwriting written in the margins, and page numbers and the like printed near the edge of the sheet are also erased.
When a header is provided near the edge of the sheet, it is often printed in white on a colored background or in color print to highlight the header text., and the area in which such a header is printed (i.e., header region) is rectangular in shape so as to form a vertically oriented rectangle. The outline of the header region comprises a side parallel to and a side perpendicular to the edges of the document. In contrast, when inferring the shape and direction of the user fingers holding the book document, the outline of the image of the user fingers or hands perpendicular to the edge of the document is extremely small, and in most cases the outline and sheet edge are inclined so as to mutually intersect.